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    <title>Document</title>
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  <body></body>
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    var a = 1;
    function foo() {
      var a = 2;
      function baz() {
        console.log(baz);
      }
      bar(baz);
    }
    function bar(fn) {
      // 这就是闭包
      fn();
    }
    foo();
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